Sometimes they find a renter that will sign a lease for a high amount only for the renter to default leaving the owner eating the vacancy. 

back then, it was not whether you would make a lot of money as mych as if there was a different purchase that would produce a better return.  

Here are some additional tips:Business Bank Account: Open a dedicated business bank account to manage income and expenses separately from personal funds.D-U-N-S Number: Register your business with Dun & Bradstreet to establish a business credit profile.

Similarly, if you put several Class D tenants in a Class A 4-plex, what do you think will happen to the property?

That is in a PERFECT WORLD.

Can be a good strategy, but my understanding is BRRRR is generally dependent on refinancing and pulling back that cash invested to repeat the next one

We have a balance of 266K on the mortgage @ 3 percent interest.

This is often achieved with written documentation, such as a formal ROW request from TxDOT or other correspondence indicating that condemnation proceedings were possible if no settlement was reached.

Refinancing  immediately prior to a sale - yes that is a cause for some seasoning. 

You need to talk with a lender first.